This mission would utilize a reusable harpoon & tether system to 'leapfrog' (uh... maybe "Spiderman" is better) between bodies by harnessing their kinetic energy in lieu of propellant.

I'm a bit skeptical, but perhaps the material and mechanical engineering types among us may weigh in as to its practicality.

Asteroids for which the surface characteristics are already known would probably not make very interesting science targets. But those with unknown surface hardness, dust accumulation, porosity, etc., would make risky targets for the harpooning technique, as Philae has recently shown. If we are talking about using 100-1000 km tethers, then various cowboy methods like lassos or bolas might be more effective. (In developing his fishing analogy, Mr. Ono has likely considered nets and hooks along with harpoons.)

I think in any case a backup plan would make sense. If the harpoon fails to stick, then expend some fuel to accomplish your science. If you become skilled at conserving the fuel, then apply for an extended mission to visit more destinations.